The energy efficiency of a vehicle depends upon a number of variables, including vehicle speed, gear state, road conditions, and vehicle load. The fuel efficiency of an internal combustion engine is dependant on the engine speed and load operating point. A vehicle traveling uphill at a given speed will consume more energy than the same vehicle traveling downhill at the same speed. A vehicle heavily loaded by an object under tow at a given speed will consume more energy than a normally loaded vehicle otherwise under the same conditions at the same speed.
Energy used to power vehicles may take the form of hydrocarbon fuels, such as gasoline, diesel or ethanol; battery charge; hydrogen fuel cells; or other forms of electrical or chemical energy. If more than one type of energy is available in a vehicle, the selections of energy to be used in various portions of travel can impact fuel efficiency. Also, energy recovery is available in many vehicular applications.
Many methods are known to evaluate current vehicle conditions. Diagnostic algorithms are known to estimate vehicle load based upon operating variables. Sensors may estimate factors internal to the vehicle including fuel grade, operator information, and maintenance history including oil change history. Sensors may evaluate traffic conditions, grade, weather conditions, and other current road conditions. Additionally, remote systems may be accessed over communications networks to evaluate conditions along a road or over a planned route, including road grade, traffic, speed limitations, existence of urban areas and traffic signals, and to forecast weather. Further processing is known to manage hybrid energy usage, evaluate operator tendencies, and track vehicle specific efficiencies.